Memory devices such as Dynamic Random Access Memories (DRAM) and Synchronous Dynamic Random Access Memories (SDRAM) are regularly used in computing systems for applications ranging from video games to personal computers.
An SDRAM usually includes components such as memory arrays, row and column decoders, and control logic. Additionally, an SDRAM typically includes a mode register for setting an operation mode so that the SDRAM can perform various functions that are optimally selected for the system containing the SDRAM. The mode register may allow external setting of operation modes; that is, it may have its set values changed in response to an externally supplied signal. An external clock signal is also used for memory devices to synchronize the operation of the memory device with other components of the computing system.
The computing systems within which SDRAMs function usually operate with a predetermined clock input which can be a single clock input or a differential clock input. While a differential clock input system may be preferable for characteristics such as low noise, some point to point systems exist where a single clock input is preferred.
To accommodate a single clock input system and a differential clock input system, SDRAMs have to be selected according to, among other features, whether or not the SDRAM's components can accommodate the clock in the system with which the SDRAM is to be used. This need for multiple types of SDRAMs imposes not only additional manufacturing costs to produce different types of SDRAMs for various systems, but also storage, distribution, and other logistical costs.
What is needed is a memory device capable of accommodating more than one clock input system, for example, a single clock input system and a differential clock input system.